)  5\ 


Ws-.s? 


V 


L^ 


yt 


Issued  AprU  24,  1915. 

HAWAII  AGRICULTURAL  EXPERIMENT  STATION, 

J.  M.  AA^ESTGATE,  Agronomist  in  Charge. 


Bulletin   No.  38. 


EFFECT  OF  FERTILIZERS  ON  THE  PHYSICAL 
PROPERTIES  OF  HAWAIIAN  SOILS. 


BY 


WILLIAM  McGEORGE, 

Assistant  Chemist. 


UNDER  THE  SUPERVISION  OP 
OFFICE   OF  EXPERIMENT   STATIONS, 

U.  S.  DEPARTMENT   OF   AGRICULTURE. 


WASHINGTON: 

GOVERNMENT  PRINTING  OFFICE. 

1916. 


s  NOV 


J»3:£S 


Issued  April  24,  1915. 

HAWAII  AGRICULTURAL  EXPERIMENT  STATION, 

J.  M.  WESTGATE,  Agronomist  in  Charge. 


Bulletin   No.  38. 


EFFECT  OF  FERTILIZERS  ON  THE  PHYSICAL 
PROPERTIES  OF  HAWAIIAN  SOILS. 


BY 


WILLIAM  McGEORGE, 

Assistant  Chemist. 


UNDER  THE  SUPERVISION  OF 

OFFICE   OF  EXPERIMENT   STATIONS, 

U.  8.  DEPARTMENT   OF   AGRICULTURE. 


WASHINGTON: 

GOVERNMENT  PRINTING  OmOE. 

1915. 


HAWAII  AGEICULTURAL  EXPERIMENT  STATION,  HONOLTJLXJ. 

[Under  the  supervision  of  A.  C.  True,  Director  of  the  Oface  of  Experiment  Stations,  United  States 

Department  of  Agriculture.] 

Walter  H.  Evans,  Chief  of  Division  of  Insular  Stations,  Office  of  Experiment  Stations. 

STATION  STAFF. 

J.  M.  Westgate,  Agronomist  in  Charge. 

J.  Edgar  Higgins,  Horticulturist. 

D.  T.  FuLLAWAY,  Entomologist. 

William  McGeorge,  Assistant  Chemist. 

Alice  R.  Thompson,  Assistant  Chemist. 

V.  S.  Holt,  Assistant  Horticulturist. 

C.  A.  Sahr,  Assistant  in  Agronomy. 

F.  A.  Clowes,  Superintendent  of  Hawaii  Substations, 

(2) 


LETTER  OF  TRANSMITTAL 


Honolulu,  Hawaii,  August  1,1914. 
Sir:  I  have  the  honor  to  submit  herewith  and  recommend  for 
pubHcation  as  Bulletin  No.  38  of  the  Hawaii  Agricultural  Experiment 
Station,  a  paper  dealing  with  the  Effect  of  Fertilizers  on  the  Physical 
Properties  of  Hawaiian  Soils,  by  William  McGeorge,  assistant  chemist 
of  this  station.  The  peculiar  constitution  of  Hawaiian  soils  makes  a 
study  of  the  physical  properties  of  these  soils  one  of  unusual  impor- 
tance. In  this  paper  there  are  described  systematic  experiments 
made  to  determine  the  effect  of  various  fertihzers  upon  capillarity, 
percolation,  flocculation,  cohesion,  apparent  specific  gravity,  vapor 
pressure,  and  hygroscopic  moisture.  Before  it  is  possible  to  reach 
a  thorough  understanding  of  Hawaiian  soils  it  has  been  found  neces- 
sary to  study  them  from  all  standpoints.  The  paper  is  a  contribu- 
tion to  the  knowledge  of  the  physical  properties  of  soils  and  particu- 
larly of  the  effect  of  fertilizers  in  other  ways  than  as  plant  food. 
Respectfully, 

E.  V.  Wilcox, 
Special  Agent  in  Charge. 
Dr.  A.  C.  True, 

Director  Office  of  Experiment  Stations, 

Z7.  S.  Department  of  Agriculture,  WasMngton,  D.  C. 

PubHcation  recommended. 
A.  C.  True,  Director, 

PubHcation  authorized. 
D.  F.  Houston, 

Secretary  of  Agriculture, 

(3) 


CONTENTS. 


Page, 

Introduction 7 

Soil  types 8 

Water  capacity  of  soils 9 

Specific  gravity 9 

Capillary  movement 9 

Effect  of  various  salts  in  molecular  proportions 12 

Effect  of  basicity  on  capillarity 16 

Percolation 17 

Flocculation 19 

Cohesion 22 

Apparent  specific  gravity 25 

Vapor  pressure 28 

Hygroscopic  moisture 29 

Sunmiary 30 


ILLUSTRATIONS. 

Page. 
Fig.  1.  Relative  capillarity  following  addition  of  salts  in  equal  quantity  and  in 

molecular  proportions 10 

2.  Effect  of  salts  and  fertilizers  on  capillary  rise  of  moisture 14 

3.  Relation  between  cohesion,  apparent  specific  gravity,  and  moisture 

content  of  soils 27 

(5) 


THE  EFFECT  OF  FERTILIZERS  ON  THE  PHYSICAL 
PROPERTIES  OF  HAWAIIAN  SOILS. 


INTRODUCTION. 

It  has  been  the  custom  in  Hawaii  since  agriculture  was  first  placed 
upon  a  commercial  basis  to  stimulate  crops  with  heavy  applications 
of  mineral  fertiUzers.  This  procedure  has  been  maintained  in  spite 
of  the  fact  that  a  majority  of  the  soils  are  naturally  well  supphed  with 
plant  food,  in  some  instances  abnormally  so. 

Hawaiian  soils  are  of  such  a  nature  that  the  maintenance  of  the  best 
possible  physical  state  is  imperative.  They  are  derived  from  the 
disintegration  of  basaltic  lava,  have  since  been  impregnated  with 
coral  limestone  in  many  of  the  lowlands  and  with  large  amounts  of 
organic  matter  in  the  uplands,  where  the  rainfall  is  high  and  the 
vegetation  profuse.  Being  derived  from  highly  basic  rocks,  the  result- 
ing soils  are  highly  basic  in  composition.  The  silica  content  varies 
from  15  to  50  per  cent,  while  the  basic  constituents,  iron  and  alumi- 
num, compose  the  major  part  of  the  remainder.  The  tendency  of 
these  metals  to  form  hydrates  or  sihcates,  their  influence  upon  the 
mechanical  structure,  drainage,  cUmatic  conditions,  temperature, 
aeration,  and  above  all  the  effect  upon  the  moisture  supply,  are  mat- 
ters which  demand  the  careful  consideration  of  agriculturists  in  these 
islands. 

Soil  moisture  is  a  prime  factor  in  successful  plant  growth.  It  not 
only  influences  the  physical  condition  but  also  acts  as  a  vehicle  for 
the  transmission  of  plant  food  from  the  soil  to  the  plant.  Since  all 
mineral  and  many  organic  substances  are  more  or  less  soluble  in 
water  and  since  all  dissolved  material  is  known  to  affect  the  physical 
properties  of  the  solvent,  it  may  be  concluded  that  the  properties  of 
soil  moisture  and  also  the  physical  condition  of  the  soil  are  partially 
dependent  upon  the  composition  of  the  soil  solution. 

These  physical  properties  include  capillarity,  percolation,  floccula- 
tion,  cohesion,  apparent  specific  gravity,  vapor  pressure,  and  hygro- 
scopic moisture.  Although  the  laboratory  determinations  of  these 
properties  of  a  soil  and  of  the  effect  of  salts  thereon  have  little 
direct  practical  value,  since  the  soil  in  such  cases  is  not  in  a  natural 
state,  and  other  conditions  are  abnormal,  they  may  be  useful  for 

(7) 


8 


studying  the  relationship  of  different  soil  types  and  the  effect  of 
fertilizers  upon  the  physical  factors  influencing  plant  growth. 

From  previous  work  in  this  laboratory  and  the  experiences  of  prac- 
tical farmers,  physical  factors  appear  to  play  a  large  part  in  the 
fertility  of  Hawaiian  soils.  The  effects  of  heat  and  volatile  antisep- 
tics, the  action  of  lime,  the  high  absorptive  power  for  fertilizers,  the 
difficulties  in  drainage,  high  cost  of  tillage,  and  the  pecuUar  biological 
effects  that  ensue,  seem  to  be  very  largely  explainable  on  a  physical 
basis  and  to  be  referable  in  part  to  coUoids. 

In  view  of  the  above  facts,  this  station  has  devoted  considerable 
time  to  investigations  upon  the  physical  properties  of  soils  and  the 
function  of  fertilizers,  other  than  as  a  source  of  plant  food,  with 
special  reference  to  the  movement  of  soil  moisture.  It  is  quite  gen- 
erally conceded  that  no  simple  explanation  of  the  influence  of  fertili- 
zers upon  the  soil  or  the  plant  is  possible. 

SOIL   TYPES. 

As  in  previous  investigations  upon  soils  in  this  laboratory,  those  of 
widely  differing  chemical  and  physical  characteristics  were  chosen. 
The  following  tables  show  the  physical  composition  and  properties 
of  these  types.  In  Table  I  wiU  be  found  the  mechanical  composition 
as  determined  by  sedimentation  according  to  Hall.^ 


Table  I. — Mechanical  analyses  of  the  soils. 

Soil  No. 

Moisture. 

Volatile 
matter. 

Fine 
gravel. 

Coarse 
sand. 

Fine 
sand. 

Silt. 

Fine  silt. 

Clay. 

428 

Per  cent. 
13.80 
12.45 
10.41 
3.58 
7.98 
12.26 
7.60 

Per  cent. 
25.65 
28.83 
17.64 
13.90 
17.81 
20.44 
13.96 

Per  cent. 

11.89 

1.70 

3.40 

Per  cent. 

28.26 

7.52 

5.29 

Per  cent. 
13.63 
14.29 
29.66 

5.76 
31.26 
31.48 

8.07 

Per  cent. 

4.64 
11.75 
10.30 
10.34 
13.39 
19.10 

9.35 

Per  cent. 
1.53 
17.49 
15.75 
37.97 
17.79 
11.93 
24.90 

Per  cent. 
0.60 

448                         

5.97 

516 

7.55 

530 

0.49 
.81 
1.50 
.36  1          1.15 

27.96 

542 

10.96 

573  . 

3.29 

574  

34.87 

Of  the  above  soil  No.  428  is  a  dark-colored,  highly  organic,  sandy 
soil  from  Glenwood,  Olaa,  Hawaii. 

Soil  No.  448  is  a  yellow  silty  sand  from  Hilo,  Hawaii. 

Soil  No.  516  is  a  sample  of  manganiferous  soil  from  the  Wahiawa 
district,  Oahu.  It  has  a  chocolate-bro^vn  color,  silty  texture,  and 
maintains  an  excellent  mechanical  condition. 

Soils  Nos.  530  and  574  are  samples  of  red-clay  soils,  the  former  of 
a  light  and  the  latter  of  a  dark  red  color. 

Soil  No.  542  is  a  titaniferous  soil  of  grayish  red  color  and  silty 
texture.     Its  physical  condition  is  very  similar  to  that  of  soil  No.  516. 

Soil  No.  573  is  a  ''dust"  soil  from  the  island  of  Hawaii.  It  is  a 
dark-colored,  highly  organic  silt,  and  very  productive. 

1  The  Soil.    London,  1908,  2.  ed.,  p.  51. 


WATER   CAPACITY   OF    SOILS. 

Table  II  contains  data  illustrating  the  water  capacities  of  these 
soils.  Columns  4  and  5  show  the  percentage  of  water  by  weight  and 
volume,  respectively,  required  to  saturate  the  soil,  and  columns  6  and 
7  show  the  percentage  by  weight  and  volume  required  to  saturate 
and  fill  interstitial  spaces. 

Table  II. —  Water  capacity  of  the  soils . 


Sou  No. 

Weight 
of  soil. 

Volume 
of  soil. 

Percentage  of  wa- 
ter to  saturate. 

Percentage  of  water 
to   saturate    and 
fill  spaces. 

Weight. 

Volume. 

Weight. 

Volume. 

428 

Gm. 
150 
150 
150 
150 
150 
150 
150 

Cc. 

177 
168 
176 
132 
160 
189 
161 

Per  cent. 
61.1 
60.2 
66.3 
43.7 
61.7 
76.3 
50.3 

Per  cent. 
51.8 
53.7 
56.5 
49.6 
57.8 
60.7 
46.9 

Per  cent. 
64.8 
64.3 
71.6 
48.3 
63.7 
76.3 
62.6 

Per  cent. 
55.1 

448                              

57  5 

516 

61.0 

530 

54.7 

542        

59.7 

573 

60.7 

574 

58.3 

SPECIFIC    GRAVITY. 

In  Table  III  are  given  the  specific  gravities,  both  real  and  apparent, 
as  well  as  the  comparative  volume  occupied  by  10  grams  of  these 
soils,  excluding  intei-stitial  spaces,'  as  determined  upon  the  air-dry 
soils. 

Table  III. — Specific  gravity  and  volume  of  the  soils. 


Soil  No. 

Real 
specific 
gravity. 

Apparent 
specific 
gravity. 

Volume 
occupied. 

Soil  No. 

Real 
specific 
gravity. 

Apparent 
specific 
gravity. 

Volume 
occupied. 

428              

2.4825 
2.5264 
2.8351 
2.9438 

0.8474 
.8929 
.8522 

1.1363 

Cc. 
4.03 
3.96 
3.53 
3.40 

542 

2. 8784 
2.4454 
2.9087 

0.9375 
.7936 
.9316 

Cc. 
3.48 

44S 

573-   .   . 

4  09 

516. 

574 

3.46 

530 

The  foregoing  data,  while  of  more  or  less  empirical  nature,  indicate 
the  variation  in  physical  properties  of  Hawaiian  types  of  soil.  The 
clays  show  the  highest  specific  gravity,  both  real  and  apparent,  the 
clay  silts  and  silts  next,  while  the  sandy  soils  show  the  lowest.  The 
opposite  relation  exists  with  regard  to  the  volume  and  water  capacity. 

CAPILLARY  MOVEMENT. 

Upon  the  capillary  movement  of  water  more  than  upon  any  other 
physical  factor  is  the  plant  dependent  for  successful  growth.  The 
functions  of  capillary  water  are  many  and  involve  the  transmission 
of  plant  food  from  the  soil  to  the  plant,  sustenance  of  the  enormous 
evaporation  during  the  heat  of  the  day,  and  the  like.  By  means  of 
81436°— Bull.  38—15 2 


10 

this  property  water  tends  to  distribute  itself  in  all  directions  through- 
out the  soil. 

There  may  be  properly  considered  to  be  three  kinds  of  water  present 
in  soils — capillary,  gravitation,  and  hygroscopic  moisture.  The 
capillary  water  is  that  which  wiU  not  drain  away  but  is  held  around 
the  soil  particles  in  the  form  of  a  moisture  film;  that  is  to  say, 
there  is  an  equilibrium  between  the  forces  of  gravity  and  surface 
tension.  However,  capillary  action  is  itself  dependent  upon  and  abso- 
lutely governed  by  such  subfactors  as  density  or  gravity,  viscosity, 
surface  tension  of  the  soil  solution,  and  the  size  and  composition  (both 
organic  and  inorganic)  of  the  soil  particles. 


Fig.  1.— Relative  capillarity  following  addition  of  salts  in  equal  quantity  and  in  molecular  proportions. 

When  an  object  is  removed  from  an  immersion  in  water  it  retains 
a  thin  film  upon  its  surface  through  the  property  of  surface  tension. 
In  the  same  manner  the  soil  particles  are  surrounded  by  a  film  or 
elastic  membrane  of  water  under  a  high  pressure,  the  thickness  vary- 
ing within  certain  limits  with  the  moisture  content  of  the  soil.  As 
water  is  lost  at  the  surface  by  evaporation  or  around  the  roots  by 
absorption,  there  is  a  movement  of  water  in  the  direction  of  in- 
creased tension,  thereby  tending  to  maintain  an  equal  distribution  of 
water.  On  the  other  hand,  viscosity,  acting  in  an  opposite  manner 
from  surface  tension,  tends  to  retard  the  movement  of  water. 

Water  in  soils  is  never  pure,  and  all  dissolved  substances  affect  the 
degree  of  surface  tension  and  viscosity  of  the  solvent.     Practically 


11 

all  inorganic  salts  increase  the  surface  tension  of  water  while  organic 
substances  decrease  it.  On  the  other  hand,  the  opposite  relation 
exists  with  regard  to  viscosity.  A  series  of  experiments  made  at  the 
Maryland  Experiment  Station  ^  upon  the  surface  tension  of  soil 
extracts  show  it  to  be  considerably  less  than  pure  water.  These  and 
many  other  facts  indicate  the  complexity  of  the  application  of  theo- 
retic principles  to  soils. 

The  capillary  power  of  a  soil  is  generally  measured  by  the  height 
to  which  water  will  rise  in  a  soil  column,  although  it  may  take  place 
in  all  directions  in  soils  and  varies  greatly  according  to  the  mechanical 
composition.  The  present  study  of  capillarity  was  carried  out  in 
1-inch  glass  tubes.  Experiments  were  made  not  only  with  soils 
but  also  with  silica  sand  and  kaolin  to  ascertain  the  relation  of 
these  materials  to  soils.  In  aU  about  40  salts,  fertilizer  materials, 
and  mixtures  were  used,  including  several  organic  manures.  As  a 
means  of  studying  the  effect  of  these  salts,  comparisons  were  made 
both  when  added  in  amounts  proportional  to  their  molecular  weights 
and  when  added  in  equal  amounts.  Also  measurements  were  made 
upon  the  variation  in  height  to  which  the  water  would  rise  as 
affected  by  amounts  of  the  salt  varying  from  0.06  to  6.66  per  cent. 
In  all  cases  the  salts  were  added  in  small  amounts. 

Before  presenting  the  data  obtained  in  these  experiments  it  is  of 
interest  to  know  the  relative  capillary  activity  of  the  soils  in  ques- 
tion. This  is  shown  in  Table  IV,  in  which  the  figures  were  obtained 
by  allowing  the  soil  column  to  stand  in  about  one-half  inch  of  water 
for  78  days. 

Table  IV. — Capillary  rise  of  water  in  the  soils. 


Soil  No. 

6 
hours. 

24 
hours. 

48 
hours. 

4 
days. 

5 
days. 

6 
days. 

7 
days. 

9 
days. 

11 
days. 

19 

days. 

32 
days. 

43 
days. 

78 
days. 

44S     

Cm. 
26.8 
22.4 
31.6 
39.  S 
36.8 
41.0 
33.7 

Cm. 
35.5 
29.1 
38.1 
51.3 
47.8 
56.6 
40.1 

Cm. 
40.9 
34.4 
42.9 
57.3 

Cm. 
46.0 
40.0 
47.3 
62.7 

Cm. 
47.8 
41.6 
49.0 
64.6 
64.0 
79.0 
45.1 

Cm. 
49.1 
42.5 
50.4 
65.9 
65.0 
81.6 
45.1 

Cm. 
50.3 
43.8 
51.5 
67.8 
66.8 
83.5 
45.1 

Cm. 
52.1 
45.2 
53.8 
70.6 
69.2 
88.4 
45.1 

Cm. 
54.0 
46.7 
55.6 
72.8 
71.2 
91.6 

Cm. 
60.4 
51.0 
58.4 
79.3 
76.4 
100.8 

Cm. 
67.0 
55.3 
62.1 
86.6 
84.8 
109.8 
50.5 

Cm. 
70.8 

■"64.' 8' 
89.8 
88.7 

1115.6 



Cm. 
82.5 

530 

71.5 

428     

76.5 

542 

100.0 

516           

55.2     62.0 
64.2     69.9 
44. 0     45. 1 

100.0 

573 

574 

63.0 

1  Top  of  column. 

The  highly  organic  silty  soil  showed  the  greatest  capillary  rise,  the 
clay  soils  least,  while  the  sandy  soils  were  intermediate. 

In  filling  the  tubes  it  is  necessary  to  exercise  considerable  care  in 
order  to  obtain  a  uniform  mixture.  This  is  made  possible  by  pro- 
jecting a  long  mre  with  a  loop  on  the  end  into  the  tube  and  withdraw- 
ing it  with  a  rotary  motion. 


1  U.  S.  Dept.  Agr.,  Weather  Bur.  Bui.  4  (1892),  p.  16. 


12 


EFFECT   OF   VARIOUS    SALTS    IN   MOLECULAR   PROPORTIONS. 

In  studying  the  relations  of  the  properties  of  salts  of  widely  varying 
molecular  composition  it  is  imperative  that  a  definite  procedure  be 
established.  With  this  idea  in  mind  the  following  curve  (fig.  1,  p.  10) 
is  presented  to  show  the  difference  in  results  obtained  when  the  salts 
were  added  in  equal  amounts  and  in  molecular  proportions  to  soil 
No.  530.  The  former  rate  was  0.5  gram  of  basic  oxid  per  100  grams 
of  soil  and  the  latter  as  follows :  Calcium  carbonate,  with  a  molecular 
weight  of  approximately  100,  was  chosen  as  a  standard  and  added 
at  the  rate  of  0.1  per  cent,  the  other  salts  in  greater  or  less  amounts 
in  proportion  to  their  molecular  weights. 

From  these  cm*ves  it  appears  that  as  a  whole  the  general  property 
of  a  given  salt  is  to  affect  the  soil  similarly  whether  added  in  equal 
weights  or  in  molecular  proportions.  This  is  at  least  true  of  the 
capillary  activity.  The  curves  throughout  are  very  similar  and  indi- 
cate that  an  increase  in  the  concentration  of  the  salt  results  in  a 
diminished  capillary  activity. 

This  variation  in  activity  as  affected  by  increasing  the  concentra- 
tion of  the  salt  suggested  a  further  study  of  the  phenomenon,  the 
results  of  which  are  given  in  Table  V.  Three  types  of  soil  and  silica 
sand  were  used  and  the  amount  of  salt  used  varied  from  none,  to  10 
grams  per  150  grams  of  soil. 


Table  V.- 

-Capillary 

rise  as  affected  by  increase  in  percentage  cf  salt  added. 

Percentage  of  salt  added. 

Salts. 

Soil  No.  530. 

Sou  No.  448. 

0.00 

0.06 

0.16 

0.33 

0.66 

3.33 

6.66 

0.00 

0.06 

0.16 

0.33 

0.66 

3.33 

6.66 

Cm. 

Cm. 

Cm. 

Cm. 

Cm. 

Cm. 

Cm. 

Cm. 

Cm. 

Cm. 

Cm. 

Cm. 

Cm. 

Cm. 

CaO 

37.3 
37.3 

34.1 
34.0 

33.2 
33.0 

32.2 
31.4 

33.5 
31.5 

18.7 
28.0 

12.5 
26.2 

30 
30 

35.0 
35.9 

36.5 
37.5 

36.0 
36.0 

37.0 
36.0 

34.0 
34.2 

29.0 

NaNOs 

33.0 

(NH4)2S04.... 

37.3 

31.9 

31.8 

28.6 

25.5 

21.1 

21.4 

30 

37.6 

35.3 

36.0 

34.2 

31.0 

29.8 

CaSoi. 

34.0 

29.8 

29.3 

29.6 

28.5 

29  8 

33.4 

30 

34.2 

34.0 

34.4 

33.2 

34.9 

36.0 

CaH(P04) 

37.3 

35.5 

37.8 

37.2 

38.8 

32.7 

23.3 

30 

34.6 

35.4 

34.9 

37.0 

38.3 

38.8 

CaCOs 

37.3 

35.  4 

33.0 

31.8 

33.8 

35.3 

38.0 

30 

33.3 

32.7 

32.2 

34.1 

35.9 

38.5 

K3PO4 

34.0 

31.0 

29.0 

25.9 

26.0 

21.7 

13.9 

30 

34.9 

33.6 

33.0 

31.4 

31.1 

24.0 

KCl 

34.0 

28.7 

27.8 

29.0 

28.0 

26.5 

26.0 

30 

34.2 

35.0 

34.4 

35.0 

36.3 

34.6 

MgS04 

37.3 

32.5 

30.6 

27.9 

27.2 

21.9 

21.7 

30 

33.1 

38.0 

34.8 

35.8 

31.0 

27.6 

NH4CI 

37.3 

31.8 

30.1 

30.5 

29.2 

26.4 

28.2 

30 

34.2 

34.2 

33.2 

35.8 

34.5 

32.3 

NajCOa 

37.3 

28.4 

24.3 

21.4 

18.7 

9.4 

6.9 

30 

32.6 

33.1 

30.1 

29.5 

17.4 

14.8 

K2SO4 

37.3 

32.3 

31.8 

30.0 

28.2 

26.0 

25.8 

30 

36.4 

36.9 

36.4 

34.8 

31.5 

31.5 

Salts. 

Sou  No.  428. 

SUica  sand. 

CaO 

29.0 
29.0 

37.0 
38.0 

36.1 
38.0 

38.0 
.37.4 

40.0 
38.0 

33.2 
35.5 

26.2 
34.8 

9  8 
9.8 

7.3 
10.9 

6.4 
12.4 

6.9 
13.7 

7.0 
13.7 

20.0 
12.1 

28.8 

NaNOa 

11.4 

Slbr::::: 

29.0 

37.9 

34.9 

34.6 

35.0 

33.5 

29.4 

9.8 

12.2 

12.6 

12.6 

12.6 

12.3 

12.0 

29.0 

37.0 

38.0 

.35.3 

38.4 

38.8 

41.2 

10.2 

12.1 

16.7 

13.0 

14.5 

22.2 

34.2 

CaH(P04) 

29.0 

38.6 

36.5 

39.0 

40.0 

38.2 

34.1 

10.2 

13.9 

16.8 

15.3 

14.4 

14.5 

18.4 

CaCOa........ 

29.0 

37.7 

38.0 

35.2 

36.3 

38.9 

37.6 

10.2 

16.6 

14.9 

18.3 

20.5 

27.4 

32.6 

K8PO4 

29.0 

38.8 

37.9 

37.0 

36.5 

33.1 

24.2 

10.2 

12.4 

14.6 

16.6 

15.7 

11.6 

12.2 

KCl 

28.0 

36.8 

36.8 

36.6 

36.9 

37.1 

35.2 

9.8 

10.9 

13.5 

11.9 

12.4 

14.1 

16.1 

MgS04 

30.7 

43.2 

42.9 

42.1 

42.8 

40.0 

36.1 

9.8 

13.9 

16.5 

13.8 

13.7 

13.7 

13.7 

NH<C1 

30.7 

41.4 

41.5 

41.2 

40.8 

37.0 

.34.9 

9.8 

11.2 

13.3 

12.3 

11.9 

10.9 

11.4 

N;i2rOj 

30.7 

30.8 

37.7 

36.1 

,39.0 

34.4 

25.4 

9.8 

15.9 

16.4 

14.7 

15.7 

17.5 

17.5 

K2SO4 

29.0 

37.2 

35.7 

34.7 

35.2 

35.2 

35.0 

9.8 

13.7 

14.1 

14.5 

13.9 

13.0 

16.2 

13 

Effect  on  soil  No.  530. — The  table  shows  that  all  the  salts,  with 
the  possible  exception  of  calcium  phosphate,  cause  a  re^jular  decrease 
in  rise  of  moisture  with  increase  in  concentration.  Calcium  phos- 
phate, when  added  at  the  rate  of  0.66  per  cent,  increases  the 
activity. 

Effect  on  soil  No.  J^Jj.8. — Here  again  the  effects  of  various  salts  seem 
to  be  related  with  few  exceptions  and  the  tendency  is  toward  an  in- 
crease in  capillarity  up  to  a  certain  concentration  beyond  which  a 
further  addition  of  the  salt  materially  retards  the  rise  of  water. 
Exceptions  to  this  rule  are  sulphate  and  carbonate  of  calcium, 
which,  being  difficultly  soluble,  w^ould  materially  change  the  physical 
nature  of  the  soil,  and  calcium  phosphate,  which,  being  a  soluble 
salt,  exerts  a  chemical  effect. 

Effect  on  soil  No.  ^28. — The  effects  of  salts  upon  the  capillary* 
activity  in  this  soil  are  similar  to  those  in  the  former  except  that  the 
variation  in  moisture  rise  is  greater.  The  soil,  containing  a  greater 
percentage  of  sand,  shows  a  higher  rise  in  moisture. 

Effect  on  silica  sand. — Conditions  in  sand  are  ideal  for  measuring 
the  effect  of  salts  upon  capillary  action  within  certain  limits,  beyond 
which  any  further  concentration  gives  misleading  results.  This  is 
due  to  the  filling  of  the  pore  spaces  and  the  subsequent  drawing  up 
of  moisture,  caused  by  the  salts  as  they  become  dissolved  by  the 
rising  moisture,  rather  than  to  the  action  of  the  salt  upon  the  activity 
of  the  film  surrounding  the  grains.  Taken  as  a  whole  the  results 
with  a  concentration  of  salt  below  3.3  per  cent  are  very  similar  to 
those  obtained  with  the  sandy  soil,  the  more  marked  variation  being 
in  the  action  of  lime. 

Apparently  the  most  important  inference  to  be  drawn  from  the 
foregoing  table  is  that  the  action  of  a  high  concentration  of  a  salt  in 
most  instances  only  magnifies  that  of  a  small  application. 

With  this  fact  determined  it  was  decided  that  the  salts  should  be 
used  in  as  small  amounts  as  possible  and  in  amounts  proportional  to 
their  molecular  weights,  thus  more  nearly  approaching  normal  con- 
dition. The  same  molecular  proportions  as  previously  mentioned 
were  used,  w^hile  the  fertifizing  substances,  such  as  mineral  phos- 
phates, blood,  etc.,  were  added  at  the  rate  of  0.1  per  cent.  The 
results  given  in  Table  VI  show  the  relation  of  various  salts  to  the  rise 
of  moisture  in  several  of  the  dominating  types  of  Hawaiian  soils. 


14 


2f/fC(i)''/S'2 


Fia.  2.— Effect  of  salts  and  fertilizers  on  capillary  rise  of  moisture. 


15 

Table  VI. — Effect  of  various  salts  and  fertilizers  on  capillarity,  the  salts  being  added  in 

molecular  proportions. 


Salts  and  fertilizers. 


K2SO4 

KCl 

KNO3 

KaPO* 

KjCOs 

CaO 

CaS04 

CaCOs 

CaHP04 

MgO 

MgS04 

MgCOs 

Na8S04 

NaCl 

N,HP04 

NajCOs 

NaNOs 

NH4CI 

(NH4)2S04 

(NH4)N03 

Acid  phosphate 

Superphosphate 

Slag 

Phosphate  rock 

Cottonseed  meal 

Blood 

Blood  and  acid  phosphate . . 
Blood  and  superphosphate . 

Blood  and  K2SO4 

Acid  phosphate  and  K2SO4. 

2(NBU)-14-2i 

2(NHi)-12-2i 

2(NH4)-l(>-2i 

l(NH4)-9-li 

l(NH4)-6-10i 

4(NH4)-ll-10i 

4.5(NH4)-23-0i 

2(N03)-14-22 

2(N03)-12-22 

Check 

Time  in  hours 


Weight 
per  200 
gm.  soil. 


Gm. 
0.35 
.15 
.20 
.42 
.28 
.11 
.27 
.20 


.24 
.70 
.28 
.12 
.72 
.21 
.17 
.11 
.26 
.16 
.20 
.20 
.20 
.20 
.20 
.20 
.20 
.20 
.20 
.20 
.20 
.20 
.20 
.20 
.20 
.20 
.20 
.20 
.20 


Soil 
No.  488. 


Cm. 
45.9 
46.6 
48.8 
42.1 
44.8 
46.6 
46.3 
47.6 
45.2 
47.5 
47.2 
44.3 
45.4 
46.5 
45.9 
45.0 
45.5 
48.9 
40.0 
47.8 
45.4 
46.5 
46.8 
45.7 
44.6 
47.6 
47.1 
47.4 
47.9 
47.9 
47.1 
47.7 
46.8 
47.5 
47.6 
46.3 
47.7 
47.6 
46.8 
35.5 
24 


Soil 
No.  530. 


Cm. 
32.7 
33.4 
33.0 
31.1 
30.2 
35.0 
33.4 
34.8 
36.9 
34.9 
31.9 
31.3 
30.5 
35.2 
29.7 
27.2 
34.2 
32.8 
31.0 
34.0 
33.9 
37.4 
37.0 
35.7 
31.4 
34.8 
34.0 
36.8 
32.8 
35.4 
35.0 
34.5 
32.8 
34.3 
34.3 
33.5 
35.5 
33.3 
33.0 
39.2 


Soil 
No.  573. 


Cm. 
55.0 
55.3 
55.  7 
54.2 
54.9 
55.5 
56.2 
56.0 
55.5 
55.1 
54.2 
55.8 
54.0 
54.5 
54.7 
54.4 
53.7 
54.7 
55.2 
54.1 
54.9 
55.2 
54.4 
54.9 
54.8 
54.2 
55.5 
54.5 
55.4 
54.6 
55.9 
56.6 
56.9 
55.8 
55.9 
54.6 
54.6 
56.0 
55.9 
55.0 
24 


Soil 
No.  516. 


Cm. 
37.1 
39.0 
36.6 
34.1 
36.5 
36.9 
38.3 
35.8 
34.5 
36.2 
36.5 
37.1 
36.4 
36.4 
30.0 
34.7 
38.0 
37.8 
37.6 
38.5 
34.5 
35.2 
.35.4 
33.6 
33.4 
35.7 
36.2 
34.9 
36.0 
35.1 
37.5 
37.3 
37.1 
37.5 
36.1 
35.9 
37.0 
35.0 
35.8 
40.4 
8 


Soil 
No.  542. 


Cm. 
39.0 
39.1 
39.8 
36.7 
38.3 
40.7 
41.4 
42.9 
40.4 
40.3 
40.4 
41.7 
38.7 
41.3 
36.9 
40.0 
40.4 
41.7 
42.1 
42.6 
40.2 
40.5 
42.3 
42.0 
37.7 
41.7 
42.5 
42.9 
41.8 
40.7 
42.4 
42.3 
40.7 
42.0 
41.2 
40.9 
40.9 
41.9 
40.8 
44.9 


Soil 
No.  428. 


Cm. 
36.4 
35.1 
36.8 
34.7 
33.5 
37.8 
38.3 
37.6 
39.2 
37.0 
37.0 
37.0 
38.6 
37.1 
39.6 
36.2 
40.3 
39.1 
37.0 
38.1 
39.5 
40.0 
40.4 
39.9 
31.4 
40.3 
40.7 
39.0 
37.4 
39.8 
41.1 
41.5 


38.3 
39.6 
37.5 
28.0 
21 


Kao- 
lin. 


Cm. 
23.6 
25.4 
24.8 
23.3 
23.6 
26.1 
21.9 
25.2 
25.6 
24.7 
25.0 
26.5 
22.1 
23.6 
20.2 
21.2 
22.8 
25.7 
24.1 
25.9 
26.0 
25.7 
26.3 


26.6 
27.4 
21.6 
26.4 
26.7 
26.5 
24.6 
24.7 
26.8 
25.5 
24.6 
26.6 
23.9 
26.4 
24.5 
28.0 
26 


Sand. 


Cm. 
15.4 
16.2 
14.6 
17.5 
17.0 
10.8 
18.9 
12.8 
15.9 
14.5 
17.5 
23.0 
21.1 
16.7 
20.3 
18.7 
14.0 
13.9 
16.5 
14.4 
15.8 
15.8 
11.8 
15.0 
9.5 
11.7 
14.2 
15.8 
12.1 
14.2 
14.8 
15.3 
14.1 
12.2 
12.9 
13.9 
13.3 
12.8 
14.2 
12.9 
24 


1  Fertilizer  mixtures  supplying  nitrogen  (in  ammonium  sulphate),  phosphoric  acid,  and  potash  in  the 
order  and  proportions  (percentages)  given. 

2  Fertilizer  mixtures  similar  to  those  referred  to  in  footnote  1  except  that  nitrogen  was  supplied  in 
sodium  nitrate. 


The  accompanying  curve  (fig.  2)  illustrates  the  effect  of  the  fertilizers 
on  capillarity  more  clearly  than  the  table. 

Effect  on  silica  sand. — Here  it  is  possible  to  explain  most  of  the 
results  by  applying  the  knowTi  effects  of  salts  upon  the  capillary 
activity  of  their  solvents.  Inorganic  salts  increase,  and  organic  sub- 
stances retard,  the  rise  of  water.  The  principal  exceptions  to  this 
rule  are  calcium  oxid  and  slag. 

Effect  on  soils  Nos.  428  and  448. — With  these  soils  the  rate  of  rise 
in  moisture  is  quite  rapid  at  first,  decreasing  to  a  very  slow  rise  in  a 
short  time.  All  organic  and  inorganic  substances  added  produced  an 
increase  in  rate  of  capillarity  within  the  time  limits  of  the  experi- 
ment. These  soils  have  a  coarse  texture,  contain  a  high  percentage  of 
organic  matter  and  of  hygroscopic  and  combined  water,  and  hence 
indicate  the  relation  of  these  properties  to  the  capillary  activity  of 
soil  extracts. 


16 

Effect  on  soil  No.  673. — This  soil,  of  all  the  types  examined,  pos- 
sessed the  greatest  capillary  activity  and  was  least  affected  by  the 
addition  of  salts.  In  fact,  it  may  be  assumed  that  the  capillary 
activity  of  this  soil  is  unaffected  by  the  addition  of  outside  agents  as 
the  results  agree  with  the  check  within  the  limits  of  experimental 
error.  In  view  of  the  above  facts,  a  series  of  experiments  was  car- 
ried out  in  which  the  amount  of  salt  added  was  doubled,  the  results 
[of  which  agreed  very  closely  with  those  reported  above. 

Effect  on  soils  Nos.  516  and  5Jf2. — These  soils  are  of  very  similar 
mechanical  composition  but  belong  to  different  chemical  types.  The 
data  presented  indicate  that  the  clay  tends  to  dominate  the  capillary 
activity  of  this  type  of  soil  in  that  the  addition  of  aU  substances 
diminished  capillarity. 

Effect  on  soil  No.  630. — The  physical  character  of  this  type  of  soil 
is  such  that  chemical  agents  would  be  expected  to  materially  affect 
its  texture.  This  theory  is  borne  out  in  the  diminished  capillary 
activity  noted  in  every  instance. 

Effect  on  Icaolin. — The  diminished  capillarity  observed  in  the  study 
of  the  effect  of  salts  on  kaolin  shows  a  direct  relationship  between 
this  substance  and  clay  soils. 

Any  attempt  at  classification  of  the  above  results  according  to 
theoretic  considerations  only  indicates  the  complexity  of  applying 
any  one  theory  to  soils.  More  than  one  factor  evidently  enters  into 
play  to  which  it  is  necessary  to  give  due  consideration.  That  fer- 
tilizers do  markedly  affect  capillarity  is  clearly  shown.  In  using 
mixed  fertilizers  there  is  little  variation  in  rise  as  related  to  variation 
in  mixture.  Those  in  which  nitrates  are  used  show  decrease  in  water 
rise  as  compared  with  those  containing  ammonium  sulphate. 

EFFECT    OF    BASICITY   ON    CAPILLARITY. 

Organic  manures,  as  compared  with  the  salts,  retard  the  rise  in  the 
sandy  soils  and  decrease  the  rise  in  others.  As  a  rule,  magnesium 
salts  affect  capillarity  less  than  the  calcium  salts,  potassium  salts  less 
than  ammonium,  sodium  less  than  potassium,  and  the  monobasic 
salts  in  most  instances  less  than  the  dibasic.  Among  the  monobasic 
salts,  carbonates  and  phosphates  show  the  lowest,  sulphates  next, 
nitrates  next,  and  chlorids  the  highest  water  line. 

With  the  phosphates  the  rise  of  moisture  seems  to  depend  upon  the 
acidity  or  basicity  of  the  salt.  This  may  be  observed  by  comparing 
data  in  Table  VII  with  those  in  Table  VI  under  the  phosphates  of 
lime.  Here  also  the  relation  between  acidity  and  rise  of  moisture  is 
similar  to  that  observed  in  the  case  of  the  potash  salt. 


17 


Table  VII. — Showing  effect  of  basicity  on  capillarity. 


K,HP04. 
KaPO*... 


Weight 
added. 


Gm. 

U.42 
1.92 
1.75 


Height. 


Cm. 
32.6 
30.3 
23.3 


KHjPOi 
KjHPO^ 
IC3PO4.. 


Weight 
added. 


Gm. 
0. 


Height. 


Cm. 
32.6 
30.9 
29.0 


1  Equivalent  to  0.5  per  cent  K2O. 

The  easily  hydrolyzable  salts,  phosphates  and  carbonates  of  the 
alkalis,  show  the  lowest  water  table.  How^ever,  they  are  much  more 
active  in  organic  soils  due  to  their  solvent  action  or  chemical  reaction 
with  the  organic  matter  present.  These  hydrolyzable  salts  also  cause 
a  swelling  of  the  clay  particles  which,  in  Hawaiian  soils,  are  partly 
composed  of  iron  and  aluminum  hydrates  and  are  conducive  to  the 
colloidal  state,  thus  closing  the  pores,  increasing  friction,  and  lowering 
the  rates  of  moisture  rise. 

PERCOLATION. 

All  moisture  which  passes  below  the  surface,  in  excess  of  that  held 
through  capillary  action  or  surface  tension,  is  subject  to  the  laws  of 
gravity.  The  rate  of  movement,  however,  is  dependent  upon  various 
factors,  such  as  the  size  and  composition  of  the  soil  particles,  height 
of  soil  surface  above  water  table,  surface  tension,  and  viscosity  of 
the  soil  solution. 

Percolation  is  quite  generally  held  to  be  most  rapid  in  soils  in 
which  capillary  activity  is  greatest,  decreasing  with  height  of  column, 
and  is  faster  in  wet  soils  than  in  dry  soils.  Clay,  of  course,  offers  the 
greatest  physical  resistance  to  the  passage  of  water  and  the  resistance 
varies  with  the  degree  of  aggregation  of  the  clay  particles. 

The  rate  with  which  water  w^ill  pass  downward,  then,  depends  upon 
the  physical  state  of  the  soil  and  this  in  turn  varies  with  the  arrange- 
ment of  the  soil  particles.  Both  of  these  properties,  however,  are 
affected  by  the  nature  of  the  soil  solution,  percolation  decreasing 
with  increase  in  concentration. 

For  studying  the  effect  of  fertilizers  upon  this  property  of  soils 
1-inch  glass  tubes  containing  soil  columns  of  about  30  centimeters 
were  fitted  up  as  in  studying  the  capillary  activity.  These  tubes 
were  connected  with  a  constant  supply  reservoir  which  maintained 
a  1-inch  head  of  water  in  the  tubes,  and  the  water  passing  through 
the  soil  was  measured  at  intervals.  The  totals  of  these  measure- 
ments are  given  in  Table  VIII. 


18 


Table  VIII. — Percolation  as  a 


by  salts  and  fertilizers . 


Salts  and  fertilizers. 


Soil 

Soil 

Soil 

No. 

No. 

No. 

530. 

573. 

428. 

Soil 
No. 
516. 


Time  of  experiment. 


6 

7 

2f 

days. 

days. 

days. 

Cc. 

Cc. 

Cc. 

1,757 

1,316 

9,212 

3,543 

1,265 

5,300 

2,602 

1,546 

4,044 

3,824 

1,555 

2,985 

940 

1,939 

2,134 

661 

1,564 

2,516 

1,902 

1,484 

2,795 

2,008 

1,504 

2,166 

4 
days. 


Salts  and  fertilizers. 


Soil 

Soil 

Soil 

No. 

No. 

No. 

530. 

573. 

428. 

Soil 
No. 
516. 


Time  of  experiment. 


days. 


7 

2f 

days. 

days. 

Cc. 

Cc. 

1,413 

2,349 

1,628 



1,253 

3,545 

1,787 

3,601 

1,189 

3,445 

1,452 

5,0.38 

1,530 

6,612 

4 

days. 


Potassium  sulphate 

Potassium  chlorid 

Potassium  phosphate 

Calcium  oxid 

Calcium  sulphate 

Calcium  carbonate 

Calcium  phosphate 

Magnesium  oxid 


Cc. 

2,312 

4,123 

3,077 

4,851 

5,635 

4,569 

5,489 

5,093 


Magnesium  sulphate. 
Blank 

Sodium  phosphate. . . 
Sodium  carbonate . . . 

Sodium  nitrate 

Ammonium  chlorid.. 
Ammonium  sulphate 


a. 

1,838 
8 

1,765 
2,021 
4,481 
4,162 
488 


Co. 
3,404 
7,086 
3,293 
2,633 
1,649 
3,355 
2,987 


Superphosphate . 


Phosphate  rock 

Cottonseed  meal 

Blood 

Blood  and  acid  phos- 
phate  

Blank 

Blood  and  potassium 
sulphate 


7 
days. 


Cc. 
1,688 
4,784 
1,990 
2,432 
1,892 

1,476 
5,865 

4,753 


7 
days. 


Cc. 
1,940 
1,588 
1,675 
1,443 
1,456 

1,567 
1,710 

1,423 


40 
hours. 


Cc. 
2,568 
3,256 
2,546 
1,924 
4,027 

2,012 
11,936 

3,526 


3 
days. 


Cc. 

1,581 

3,632 

3,902 

4,659 

3,656 

3,324 
2  7,226 

1,715 


Potassium  sulphate  and 

acid  phosphate 

2(NH4)-14-2  3 

1(NH4)-^13 , 

4(NH4)-11-10  3 

4.5(NH4)-23-0  3 

2(N03)-14-24 , 

Acid  phosphate 


7 

7 

40 

days. 

days. 

hours. 

Cc. 

Cc. 

Cc. 

3,491 

1,321 

2,693 

2,305 

1,618 

1,945 

3,685 

1,636 

3,852 

2,763 

1,331 

1,365 

3,198 

1,381 

2,076 

3,745 

1,480 

2,044 

3,209 

1,649 

1,308 

3 
days. 


Cc. 

4,631 
4,060 
2,847 
3,239 
4,826 
5,006 
2,456 


1  Stopped  after  2f  days. 

2  Stopped  after  2  days. 

'  Fertilizer  m.ixtures  supplying  nitrogen  (in  ammonium  sulphate),  phosphoric  acid,  and  potash  in  the 
order  and  proportions  (percentages)  given. 

4  Fertilizer  mixture  similar  to  those  referred  to  in  footnote  3  except  that  nitrogen  was  supplied  in 
sodium  nitrate. 

A  glance  at  this  table  clearly  indicates  the  complexity  of  the  study 
of  the  passage  of  water  through  soils.  It  is  quite  generally  conceded 
that  those  soils  in  which  capillary  activity  is  greatest  offer  the  least 
resistance  to  the  passage  of  water.  Soil  No.  573  fails  to  lend  sup- 
port to  this  theory,  as  does  also  No.  516.  In  these  soils  the  capillary 
activity  is  greatest,  while  they  offer  much  greater  resistance  to  the 
passage  of  water  than  the  sandy  soils.  Even  the  heavy  clay  soil 
offers  less  resistance  than  No.  573. 

As  a  whole  the  calcium  salts  cause  less  resistance  than  magnesium 
salts,  ammonium  less  than  potassium,  chlorids  less  than  sulphates  in 
clay  soils,  but  the  sulphates  least  in  organic  soils.  Mixtures  in  which 
sodium  nitrate  is  used  cause  less  resistance  to  flow  of  water  than 
where  ammonium  salts  were  used. 

Soil  No.  530. — All  the  salts  and  fertilizers  added  to  this  type 
retarded  the  percolation  of  water.  There  is  a  sHght  relation  between 
the  degree  of  resistance  and  the  flocculating  power  of  the  salts.  As  a 
rule  the  most  deflocculated  samples  were  among  those  that  offered 
the  greatest  resistance  and  vice  versa,  as  was  found  by  examining 


19 

the  soils  at  the  completion  of  the  experiments.  The  organic  manures 
resist  the  flow  also  but  when  mixed  with  mineral  fertilizers  the 
resistance  is  less.  The  data  taken  from  daily  observations,  not  in- 
dicated in  the  table,  show  that  the  passage  of  water  in  practically 
all  the  tubes  decreased  steadily  from  day  to  day  after  the  salts 
became  diffused  throughout  the  soil  and  the  clay  began  to  swell. 
This  applies  only  to  soils  Nos.  530  and  573. 

Soil  No.  573. — Percolation  through  this  soil  was  very  slow  and 
regular.  Like  capillary  activity,  salts  had  very  little  effect  upon  it. 
The  amount  of  water  passing  through  the  tubes  was  less  on  the  last 
day  of  the  experiment  than  on  the  first  day.  There  is  practically  no 
clay  present  in  this  soil,  so  that  the  action  of  the  salts  is  probably 
upon  the  organic  matter.  This  soil  is  the  only  one  in  which  any  salt 
increased  the  rate  of  flow.  These  salts  were  calcium  sulphate, 
sodium  carbonate,  and  superphosphate.  Sodium  nitrate  strongly 
retarded  percolation. 

Soil  No.  Jf.28. — In  this  instance  it  was  not  possible  with  the  equip- 
ment available  to  maintain  a  constant  head  of  water,  due  to  the  large 
volume  which  would  percolate  during  the  night.  All  the  materials 
used  at  first  decreased  the  rate  of  percolation  but  the  daily  rate 
increased  steadily,  for  which  reason  the  series  was  not  carried  out  so 
completely  as  in  the  two  previous  soils.  This  increase  was  probably 
due  to  a  washing  out  of  the  substances  added.  The  action  of  sodium 
carbonate  and  sodium  nitrate  was  very  similar  and  unhke  the  effects 
in  the  above  organic  soil.  The  organic  manures  resist  percolation 
quite  strongly.  The  calcium  and  magnesium  salts  offer  the  greatest 
resistance,  sodium  salts  next,  ammonium  salts  next,  and  potash  salts 
the  least. 

Soil  No.  516. — This  soil,  owing  to  its  mechanical  condition  and 
low  organic  content,  offers  little  resistance  to  percolation  of  water. 
The  effect  of  adding  any  agent  is  to  decrease  the  flow.  However,  the 
results  obtained  indicate  that  some  soils  are  capable  of  restoring  their 
equihbrium,  as  is  shown  by  the  fact  that  the  depression  of  the  first 
day  became  less  as  diffusion  became  more  complete.  The  dibasic 
salts  offer  less  resistance  to  percolation  than  the  monobasic. 

FLOCCXJLATION. 

The  r6le  of  flocculation  in  soils  is  one  of  considerable  importance 
in  a  study  of  soils  such  as  occur  in  these  islands.  The  red  clay  is  a 
type  possessing  an  unusual  tenacity  and  requires  judicious  handling 
to  prevent  puddling  and  to  maintain  the  colloidal  clay  in  the  best 
physical  condition.  Various  investigators,  recognizing  that  a  solu- 
ble salt  wiU  bring  about  the  flocculation  of  the  suspended  material 
in  a  turbid  liquid,  have  studied  the  relation  of  this  to  the  improve- 


20 

ment  of  the  texture  in  heavy  soils.  Indeed  this  is  said  to  be  the 
primary  function  of  hme,  which  is  one  of  the  most  universally  applied 
soil  amendments. 

The  above  studies  indicate  that  the  maintenance  of  a  crumb 
structure  is  seriously  menaced  by  the  presence  of  even  a  trace  of 
certain  compounds.  Hence  flocculating  or  deflocculating  agents 
alter  the  soil  structure.  The  latter  not  only  destroy  the  compound 
aggregates  but  also  bring  about  a  diffusion  or  swelling  of  the  coUoidal 
clay.  This  results  in  a  closing  of  the  pore  spaces,  shutting  out  the 
air,  development  of  acid  conditions,  and  menacing  the  whole  cycle  of 
normal  soil  transformations. 

Since  it  is  conceded  that  the  best  physical  state,  known  as  a  crumb 
structure,  is  due  to  flocculation  of  the  smaller  grains  into  aggregates, 
the  conclusion  is  obvious  that  the  study  of  conditions  conducive  to 
the  formation  of  a  colloidal  state  and  the  relation  of  salts  to  this 
state  may  be  of  considerable  local  application. 

As  a  means  of  studying  this  property  of  Hawaiian  clay  a  sample 
of  highly  puddled  soil  was  chosen,  one  in  which  the  clay  would 
remain  in  suspension  for  weeks.  A  stock  suspension  of  this  soil 
sufficient  for  all  experiments  was  prepared,  so  that  a  suspension  of 
known  concentration  would  be  available.  The  degree  of  floccula- 
tion, to  a  certain  extent,  depends  upon  the  relation  of  the  amount  of 
clay  in  suspension  to  the  strength  of  the  flocculating  agent. 

Normal  solutions  were  prepared  of  all  the  salts  used  in  previous 
experiments,  except  the  slightly  soluble  ones,  in  which  case  saturated 
solutions  were  made.  By  a  series  of  preliminary  experiments  those 
salts  having  a  negative  or  deflocculating  effect  were  eliminated. 
These  include  potassium  and  sodium  phosphates  and  carbonates. 
Secondly,  salts  causing  a  flocculation  of  the  clay  but  not  sufficiently 
soluble  to  form  a  normal  solution  were  eliminated.  These  include 
the  oxid,  carbonate  and  sulphate  of  calcium  and  the  oxid  and  car- 
bonate of  magnesium. 

The  comparisons  were  made  in  glass  cylinders  of  400  cubic  centi- 
meters capacity  in  which  were  placed  2  cubic  centimeters  of  normal 
salt  solution,  10  cubic  centimeters  of  clay  suspension,  and  188  cubic 
centimeters  of  water,  making  a  total  of  200  cubic  centimeters.  This 
mixture  was  shaken  and  allowed  to  settle.  In  the  case  of  the  stronger 
flocculants  this  proved  too  great  a  concentration,  hence  the  experi- 
ments were  repeated  with  a  much  weaker  solution.  The  results  are 
given  in  Table  IX. 


21 


Table  IX. — Showing  relative  rate  of  Jlocadation  by  acids  and  their  salts. 


Salt  or  acid. 


H,S04..-. 

Al2(S04)3. 

CaS04.... 
MgS04.... 
K^04.... 
NasS04... 
(NH4)sS0 

HCl 

CaClj 

MgCl, 

KCl 


Time  required  for 
flocculation. 


T^normal 
solution. 


Hours. 

1 

1 

9 

4 

105 

120 

147 

1 

1 

3 

165 


^J^normal 
solution. 


Hours. 


Salt  or  acid. 


NaCl 

NH4CI 

HNO3 

Ca(N0,)2.. 
Mk(N03)2.. 

KNO3 

NaNOs.... 
NH4N03... 

H3PO4 

CaHP04..- 
CH3COOH 


Time  required  for 
flocculation. 


T^normal 
solution. 


Hours. 

120 

103 

1 

1 

2J 
48 
150 
72 
li 
li 
15 


^i^normal 
solution. 


Hours. 


2 
72 
144 


192 


I 


These  results  agree  to  a  certain  extent  with  the  findings  of  other 
investigators.  They  indicate  a  relationship  between  the  valency  of 
the  salt  and  its  flocculating  power.  The  most  active  salt  is  aluminum 
sulphate,  a  trivalent  salt  and  one  which  is  highly  hydrolyzed.  The 
divalent  calcium  and  magnesium  salts  of  nitric,  hydrochloric,  and 
sulphuric  acids  are  next,  while  the  monovalent  salts  of  sodium, 
potassium,  and  ammonium  are  least  active.  The  acids  are  stronger 
than  any  of  their  divalent  salts  but  the  trivalent  salt,  aluminum  sul- 
phate, is  stronger  than  any  of  the  acids.  Nitric  acid  is  the  strongest, 
hydrochloric  second,  and  sulphuric  third.  Likewise  the  nitrates  and 
chlorids  are  stronger  than  the  sulphates.  This  indicates  that  the 
degree  of  flocculation  is  related  both  to  the  acidity  and  the  basicity. 
Phosphoric  and  acetic  acids  cause  much  less  flocculation  than  the 
other  acids. 

Thus  far  no  investigator  has  been  able  to  satisfactorily  explain 
this  phenomenon,  although  various  theories  have  been  advanced/ 
The  explanation  is  probably  to  be  found  within  the  realm  of  collofd 
chemistry.  Hall  and  Morrison  suggest  that  some  physicist  must  first 
arrive  at  a  satisfactory  explanation  of  Brownian  motion.  They* 
have  recently  suggested  the  possible  presence  of  free  alkali  derived 
from  the  partial  hydrolysis  of  the  suspended  material  and  that  floc- 
culation ensues  when  these  are  neutralized.  Hilgard  assumed  a  chem- 
ical hydration  of  the  fine  particles  of  clay  when  in  suspension  which 
when  lime  was  added  became  dehydrated,  causing  a  flocculation  of 
the  soil  particles. 

Regarding  the  composition  of  soil  colloids  Uttle  is  known.  While 
many  authors  have  assumed  them  to  be  inorganic  it  is  probable  that 
being  characteristic  of  the  states  of  matter  from  which  they  are 
formed  and  not  of  any  particular  substance,  they  may  be  partly 
organic.  Free^  suggests  that  organic  colloids  may  coat  the  soil 
particles  with  thin  films. 

1  Jour.  Agr.  Sci.,  2  (1907),  No.  3,  pp.  244-256. 

a  Jour.  Franklin  Inst.,  169  (1910),  No.  6,  pp.  421-438;  170  (1910),  No.  1,  pp.  46-57. 


22 

There  is  practically  no  doubt  that  colloids  exist  in  Hawaiian  soils. 
The  physical  properties  indicate  such  to  be  the  case.  A  chemical 
analysis  of  the  clay  shows  it  to  be  primarily  a  silicate  of  iron  and 
aluminum  with  a  probabihty  of  the  hydrates  being  present  also. 
Noncoagulable  clay,  by  analysis,  shows  a  higher  percentage  of  iron 
and  silica  and  less  alumina  than  the  coagulable  clay.  This  indicates 
that  part  of  the  iron  exists  in  the  form  of  ferric  hydrate. 

While  the  chemical  composition  may  affect  the  nature  of  the  colloids 
and  the  degree  of  flocculation  the  phenomenon  itself  is  physical. 
The  relation  is  between  the  composition  and  nature  of  the  colloidal 
film  surrounding  the  clay  particle  and  its  degree  of  surface  tension. 
The  effects  of  any  added  acid  or  salt  is  to  alter  the  nature  of  the  film 
probably  through  penetration  or  chemical  action,  thereby  increas- 
ing or  decreasing  the  surface  tension,  depending  on  the  nature  of  the 
added  substance,  and  increasing  or  decreasing  the  degree  of  floccula- 
tion. Some  authors  maintain  that  the  salt  or  acid  actually  replaces 
bases  within  the  colloid,  thereby  altering  its  composition,  while  others 
maintain  that  it  only  alters  the  film  and  by  washing  upon  a  filter 
with  water  the  clay  wiU  revert  to  its  original  colloidal  state.  This 
latter  contention  seems  to  apply  best  to  the  conditions  found  to  exist 
in  Hawaiian  soils.  At  all  events  the  flocculation  of  Hawaiian  clay 
is  influenced  as  follows : 

(1)  Most  acids  and  neutral  salts,  especially  electrolytes,  increase 
the  degree  of  flocculation. 

(2)  Highly  dissociated  acids  are  the  strongest  coagulants,  and  the 
less  dissociated  acids  act  more  or  less  in  proportion  to  their  degree  of 
ionization. 

(3)  Electrolytes  of  greater  valency  possess  a  greater  degree  of 
flocculation  than  those  of  lesser  valency. 

(4)  Most  highly  dissociated  alkaUs  are  strongest  deflocculants,  as 
are  also  the  alkah  salts  of  weak  acids,  such  as  phosphoric. 

(5)  Ammonium  hydroxid  is  an  exception,  being  only  slightly 
ionized,  but  at  the  same  time  it  is  the  strongest  deflocculant. 

(6)  The  degree  of  flocculation  depends  upon  the  strength  or  valency 
of  the  anion  as  well  as  of  that  of  the  cation. 

COHESION. 

The  film  of  moisture  around  soil  particles  imparts  to  them  cohesion 
by  which  the  particles  are  bound  together.  As  the  moisture  content 
decreases  surface  tension  of  the  film  increases  and  the  particles  are 
drawn  together.  Hence,  in  a  clay  soil  where  shrinkage  is  greatest, 
there  results  the  formation  of  cracks.  There  is  a  definite  moistm-e 
content  at  which  tenacity  of  the  soil  particles  is  at  a  minimum,  the 
texture  is  best  for  culture,  and  the  whole  environment  is  most  con- 
ducive to  the  best  plant  growth.     The  factors  bringing  about  such 


23 

conditions  depend  upon  the  mechanical  composition,  the  organic 
matter  present,  and  the  presence  or  absence  of  certain  soluble  sub- 
stances. 

As  a  means  of  measuring  the  effect  of  salts  upon  this  cohesive 
property  of  Hawaiian  soils,  the  procedure  described  by  the  Bureau  of 
Soils  was  used.^  In  this  procedure  a  mechanical  shaker  having 
a  screening  apparatus  and  operated  by  a  motor  is  used  to  insure  a 
uniform  packing  of  the  soil.  By  means  of  this  apparatus  a  cup  was 
filled  with  the  soil  and  by  means  of  a  penetratmg  apparatus  the  weight 
necessary  to  cause  a  steel  cone-shaped  needle  to  penetrate  a  fixed 
depth  was  determined.  While  the  results  so  obtained  are  not  directly 
comparable  with  results  obtained  by  other  investigators,  due  to  slight 
differences  which  may  result  from  the  construction  of  the  apparatus, 
they  are  comparable  among  themselves. 

In  Table  X  are  shown  the  salts  used  in  the  experiments  and  the 
penetration  with  varying  moisture  contents,  1,500  grams  of  soil 
being  used  in  making  the  determinations.  After  each  penetration 
water  was  added,  as  shown  in  the  table,  weU  mixed  with  the  soil  and 
allowed  to  stand  one  hour  before  repeating  the  penetration  test.  Five 
penetrations  were  made  on  each  cup  of  soil  and  the  average  taken. 
The  cup  was  refilled  for  further  penetrations,  repeating  these  some 
three  or  more  times  at  each  moisture  content  if  there  was  any  undue 
variation.  Water  was  added  up  to  the  point  at  which  it  was  impos- 
sible to  work  the  soil.  Salts  were  added  at  the  rate  of  15  grams  per 
1,500  grams  soil,  or  1  per  cent  of  salt.  Portions  were  taken  from 
each  cup  for  moisture  determination. 

Table  X. — Effect  of  salts  on  cohesion  in  soils  under  various  percentages  of  moisture. 

SOIL  NO.   573. 


Check. 

Potassium 

Calcium 

Superphos- 

AmmoTiium 

Sodium 

Sodium 

sulphate. 

oxid. 

phate. 

sulphate. 

nitrate. 

carbonate. 

<D 

a 

<s 

a 

o 

a 

<D 

a 

<D 

fl 

<9 

a 

<D 

a 

o    . 

(h       , 

ti     . 

o 

o 

o    . 

o 

-1 

11 

5s 

1.1 

.""S 

-1 

11 

II 

P 

II 

31 

If 

o8 

g^ 

o  § 

S^ 

o?, 

§  ^ 

o8 

^^ 

o  3 

^^ 

2.^ 

g^ 

^^ 

?^ 

S 

(^ 

a 

(S 

s 

Ph 

S 

Ph 

1^ 

Clh 

a 

p^ 

a 

(U 

Perct. 

Gm. 

Perct. 

Gm. 

Perct. 

Gm. 

Perct. 

Gm. 

Perct. 

Gm. 

Perct. 

Gm. 

Perct. 

Gm. 

13.43 

25.25 
27.25 

16.67 

15.61 

26.25 

15.85 

26.35 

15.55 

29.20 

15.43 

28.60 

14.55 

28.55 

16.94 

27.30 

20.65 

28.85 

19.14 

26.25 

17.62 

27.55 

17.60 

30. 15 

17.87 

27.50 

18.05 

29.95 

19.26 

27.35 

23.14 

26.90 

21.94 

25.15 

20.40 

28.8 

21.22 

29.15 

20.54 

27.7 

21.10 

27.40 

21.70 

27.15 

25.11 

25.00 

24.72 

25.20 

22.96 

28.25 

23.02 

26.35 

23.15 

27.05 

23.78 

25.25 

24.07 

27.30 

I 


SOIL  NO.  530. 


3.66 
6.78 
9.98 
12.66 
16.40 
19.30 


50 

48.75 
46.25 
49.  30 
51.50 
48.5 


3.90 
7.14 
11.43 
14.84 
16.86 
21.68 


50.0 
46.9 
49.3 
55.2 
52.0 
51 


8.35 
11.61 
14.50 
17.10 
21.60 


51.5 

48.6 
49.7 
52.2 
47.0 


7.47 
10.50 
14.44 
17.42 
19.86 


48.2 

51.75 

53.5 

52.45 

47.45 


7.47  I  50.6 
11.69  I  51.5 


15.02 
17.33 
20.20 


53.45 

49.7 

48.55 


8.56 
12.56 
14.87 
18.00 
20.31 


52.75 

51.5 

49.9 

50.4 

47.95 


7.47 
11.02 
13.88 
16.76 


49.2 
58.75 
61.0 
69.0 


1 U.  S.  Dept.  Agr.,  Bur.  Soils  Bui.  50  (1908). 


24 


Table  X. — Effect  of  salts  on  cohesion  in  soils  under  various  percentages  of  moisture- 
Continued. 

SOIL  NO,  516. 


Check. 

Potassittm 

Calcium 

Superphos- 

Ammonium 

Sodium 

Sodium 

sulphate. 

oxid. 

phate. 

sulphate. 

nitrate. 

carbonate. 

© 

fl 

<D 

^ 

<D 

Pi 

<D 

a 

® 

^ 

<D 

0 

<o 

a 

>H         • 

U      • 

ii     • 

^^    • 

^"3 

4J  CO 

00  ■g 

C3rd 

5| 

11 

'=''3 

05   iD 

5S 

is 

51 

1.1 

11 

o  § 

^^ 

o  § 

n^^ 

og 

g^ 

o^ 

g^ 

o^ 

g^ 

o^ 

g^ 

Z^ 

g^ 

^ 

Ph 

s 

^ 

^ 

(^ 

^ 

(^ 

!^ 

^ 

1^ 

Ph 

§ 

^ 

Per  ct. 

Gm. 

Perci. 

Gm. 

Perct. 

Gm. 

Perd. 

Gm. 

Perct. 

Gm. 

Perrt. 

Gm. 

Per  cf . 

(?TO. 

10.95 

38.5 
36.65 

15.14 

14.19 

35.95 

12.33 

39.4 

13.09 

35.90 

11.49 

35.3 

10.19 

37.15 

12.18 

35.6 

18.54 

36.3 

17.77 

37.15 

15.96 

38.3 

16.51 

35.9 

15.01 

39.8 

13.98 

39.30 

15.62 

36.9 

21.26 

38.45 

21.16 

35.0 

19.12 

38.35 

19.11 

36.2 

18.22 

37.45 

17.46 

36.5 

18.79 

35.65 

24.13 

37.5 

23.67 

33.3 

21.71 

40.05 

22.46 

39.55 

21.86 

39.5 

20.90 

36.95 

21.25 

37.45 

26.71 

33.9 

26.11 

32.55 

24.77 

35.60 

24.95 

34 

22.21 

37.45 

22.79 

36.1 

23.37 

37.05 

SOIL  NO.  428. 


11.23 

37.85 

35.40 

31.6 

31.75 

30.3 

28.4 

15.11 

12.97 
16.42 
19.10 
21.98 
24.96 

34.6 

35.95 

35.0 

33.1 

31.15 

14.44 
18.39 
20.00 
22.75 
26.62 

35.1 

32.95 

34.5 

31.25 

30.5 

13.14 
17.30 
19.50 
22.42 
25.34 

36.6 

35.25 

34.4 

33.05 

32.75 

14.18 
18.08 
20.76 
23.25 

25.87 

37.05 

17.96 

33.95 

18.50 

34.7 

21.90 

. 

35.25 

25.33 

32.1 

Soil  No.  573;  given  in  Table  X,  is  the  silty  organic  soil.  The  weight 
required  for  penetration  increased  at  first  and  then  decreased  with 
increase  in  moisture  content,  reaching  a  minimum  at  25  per  cent, 
which  is  apparently  the  optimum  moisture  content  for  this  type  of 
soil.  The  effect  of  the  addition  of  salts  is  to  increase  the  weight  nec- 
essary for  penetration  at  the  optimum  moisture  content,  that  is,  salts 
increase  the  cohesion  of  the  soil  particles.  This  is  especially  true  of 
lime.  The  cohesion  apparently  does  not  vary  with  change  in  moisture 
content  in  the  presence  of  sodium  carbonate. 

Soil  No.  530. — Table  X  shows  the  relation  between  moisture  con- 
tent and  cohesion  for  the  predominating  red  type  of  clay  soil.  Nine- 
teen per  cent  moisture  represents  the  point  above  which  it  is  impossi- 
ble to  work  with  this  type,  due  to  the  fact  that  the  soil  will  not  pass 
through  the  screen  used  in  the  apparatus.  The  figures  obtained 
show  an  optimum  moisture  content  of  about  1 0  per  cent  if  conclusions 
are  to  be  drawn  from  the  theories  advanced  by  previous  investigators. 
However,  10  per  cent  is  rather  low  for  this  type  of  soil  and  it  is  prob- 
able that  the  optimum  point  for  plant  growth  is  above  the  range  of 
the  experiment.  The  cohesion  of  this  soil  decreases  at  first,  then 
increases  up  to  16  per  cent  moisture,  followed  by  a  second  decrease. 
The  remarkable  effect  of  sodium  carbonate  (and  this  would  apply  in 
more  or  less  degree  to  all  deflocculating  agents)  is  clearly  shown  in  the 
table.  Regarding  the  effect  of  other  salts,  little  can  be  concluded  from 
the  data  at  hand.  That  they  do  affect  cohesion  there  is  no  doubt,  but 
it  is  impossible  to  definitely  classify  these  effects. 


25 


Soil  No.  516. — Here  again  it  was  not  possible  to  determine  exactly 
the  optimum  point,  but  26  per  cent  water  is  probably  very  close  to  this 
stage.  The  effect  of  increasing  the  moisture  content  is  to  decrease 
cohesion  to  a  certain  point,  followed  by  an  increase,  then  descending 
as  the  optimum  moisture  content  is  approached.  Potassium  sulphate 
decreases  cohesion  while  the  rest  of  the  salts  apparently  increase  this 
property  in  varying  degree. 

Soil  No.  428. — The  effect  of  varying  the  moisture  content  of  this 
soil  differs  from  that  observed  with  the  other  soils  in  that  the  de- 
crease in  cohesion  is  regular  and  rapid  as  a  result  of  increasing  the 
moisture  content  up  to  the  optimum  point.  The  effect  of  salts  is  to 
increase  the  cohesion  of  this  type  of  soil.  This  fact  was  found  to  be 
true  in  every  instance.  Owing  to  a  lack  of  sufficient  soil,  ammonium 
sulphate  and  sodium  nitrate  were  not  used. 

Throughout  this  work  care  was  exercised  to  subject  each  cup  of  soil 
to  the  same  procedure.  Penetrations  were  made  at  equal  distances 
from  the  center  of  the  cup,  the  weight  was  allowed  to  fall  through 
equal  heights,  and  similar  methods  used  throughout.  Even  with 
these  precautions  it  was  difficult  to  obtain  closely  agreeing  results 
from  a  clay  soil,  but  very  concordant  results  were  obtained  from 
the  other  types. 

APPARENT  SPECIFIC  GRAVITY. 

Closely  related  to  cohesion  and  bearing  directly  on  the  swelling  of 
soils  on  wetting  and  shrinking  and  cracking  upon  drying  is  the  appar- 
ent specific  gravity,  the  relation  between  the  weight  of  a  soil  and  the 
volume  it  occupies.  This  property  has  been  supposed  to  be  at  a 
minimum  at  the  optimum  moisture  content  of  the  soil.  Like  all 
physical  properties  it  is  subject  to  modification  and  is  more  or  less 
affected  by  the  same  factors  that  affect  the  cohesive  power. 

The  same  apparatus  used  for  penetration  experiments  was  used  for 
the  determination  of  the  apparent  specific  gravity.  The  data  were 
obtained  by  dividing  the  weight  of  the  soil  in  the  container  by  its 
volume.     The  results  are  given  in  Table  XI. 

Table  XI. — Effect  of  salts  and  moisture  content  on  apparent  specific  gravity. 

SOIL  NO.  573. 


Check. 

Potassium 

Calcium 

Superphos- 

Ammonium        Sodium 

Sodium 

sulphate. 

oxid. 

phate. 

sulphate.            nitrate. 

carbonate. 

Ap- 

Ap- 

Ap- 

Ap- 

Ap.   1 

Ap- 

Ap. 

Moist- 

parent Moist- 

parent 

Moist- 

parent 

Moist- 

parent Moist-  parent  Moist- 

parent 

Moist- 

parent 

ure 

SRf- 

ure 

spe- 

ure 

spe- 

ure 

spe- 

ure 

spe- 

ure 

spe- 

ure 

sp^e- 

con- 

cific 

con- 

cific 

con- 

cific 

con- 

cific 

con- 

cific 

con- 

cific 

con- 

ciflc 

tent. 

grav- 

tent. 

grav- 

tent. 

grav- 

tent. 

grav- 

tent. 

grav- 

tent. 

grav- 

tent. 

grav- 

ity. 

ity. 

ity. 

ity. 

ity. 

ity. 

ity. 

Perct. 

Perct. 

Perct. 

Perct. 

Perct. 

Perct. 

Perct. 

13.43 

0. 7017 

16.67 

.6745 

io-ei   6.6807 

is.  85 

0.6842 

15.55 

0.6868 

15.43 

0.6587     14.55 

0.6693 

16.94 

0.6605 

20.65 

.  6359     19. 14 

.6305 

17.62 

.6605 

17.60 

.6544 

17.87 

.6394!    18.05 

.6394 

19.26 

.6412 

23.14 

.6000     21.94 

.5021 

20. 4C 

.6254 

21.22 

.6193 

20.54 

.6061 

21.10 

.5894 

21.70 

.6079 

26.11 

24.72 

.5438 

22.96 

.5842 

23.02 

.5710 

23.15 

.5674 

23.78 

.5587 

24.07 

.5649 

26 


Table  XI. — Effect  of  salts  and  moisture  content  on  apparent  specific  gravity — Contd. 

SOIL  NO.  530. 


Check. 

Potassium 

Calcium 

Superphos- 

Ammonium 

Sodium 

Sodium 

sulphate. 

oxid. 

phate. 

sulphate. 

nitrate. 

carbonate. 

Ap- 

Ap- 

Ap- 

Ap- 

Ap- 

Ap- 

Ap- 

Moist- 

parent 

Moist- 

parent 

Moist- 

parent 

Moist- 

parent 

Moist- 

parent 

Moist- 

parent 

Moist- 

parent 

ure 

spe- 

ure 

spe- 

ure 

spe- 

ure 

spe- 

ure 

spe- 

ure 

spe- 

ure 

spe- 

con- 

cific 

con- 

cific 

con- 

cific 

con- 

cific 

con- 

cific 

con- 

cific 

con- 

cific 

tent. 

grav- 

tent. 

grav- 

tent. 

grav- 

tent. 

grav- 

tent. 

grav- 

tent. 

grav- 

tent. 

grav- 

ity. 

ity. 

ity. 

ity. 

ity. 

ity. 

ity. 

Perct. 

Perct. 

Perct. 

Perct. 

Perct. 

Perct. 

Perct. 

3.66 

1.0284 
1.0596 

3.90 
7.14 

1. 0368 
1.0737 

6.78 

8.35 

1.0745 

7.47 

1.0622 

7.47 

1.0500 

8.56 

1.0517 

7.47 

1.0087 

9.98 

1.0886 

11.42 

1.0973 

11.61 

1.1135 

10.50 

1.0851 

11.69 

1.0956 

12.52 

1. 1052 

11.02 

1.0517 

12.66 

1.1096 

14.84 

1. 1289 

14.50 

1.1509 

14.44 

1. 1079 

15.02 

1.1043 

14.87 

1. 1079 

13.88 

1.0394 

16. 4C 

1. 1017 

16.86 

1.1114 

17.  IC 

1. 107C 

17.42 

1.0912 

17.33 

1.0605 

18.00 

1.0693 

16.76 

1.0079 

19.30 

.9640 

21.68 

.9745 

21.60 

.9096 

19.86 

.9447 

20.20 

.8789 

20.31 

.9184 

SOIL  NO.  516. 


10.95 
15.14 
18.54 
21.26 
24.13 


0.8035 
.8973 


.8219 
.7403 


14.19 
17.77 
21.16 
23.67 


0.9026 
.9219 
.8140 
.7517 


12.33 
15. 

19.12 
21.71 


.9351 

.8886 
.8035 


13.09 
16.51 
19.11 
22.46 


26.71  .6675  26.11  .6833  24.77  .7210  24.95  .7140  22.21  .7543  22.79  .7552 


0.8859 
.9158 
.8570 

.7781 


11.49 
15.01 

18.22 
21.86 


.9245 
.8982 
.8219 


10.19 
13.98 
17.46 
20.90 


0.8684 
.9236 
.9166 
.8307 


12.18 
15.62 
18.79 
21.25 
23.37 


0.8587 
.9035 
.8833 
.8324 
.7912 


SOIL  NO.  428. 


11.23 
15.11 
17.96 
18.50 
21.90 
25.33 


0.7394 


.7464 
.7175 
.6737 
.6403 


12.97 
16.42 
19.10 
21.98 
24.86 


0.7403 
.7342 
.7079 
.6780 
.6377 


14.44 
18.39 
20.00 
22.75 
26.62 


0. 7517 

.7245 
.7079 


13.14 
17.30 
19.50 
22.42 
25.34 


0.7245 
.7166 
.7008 
.6701 
.6623 


14.18 
18.08 
20.76 
23.25 
25.89 


0.8386 
.7657 
.7298 
.6929 
.6666 


In  soil  No.  573  specific  gravity  decreases  regularly  with  increase 
in  moisture  content  up  to  the  optimum  both  in  the  untreated  soil  and 
in  those  treated  with  salts.  The  effect  of  salts  is  not  striking  but  in 
some  cases  increases,  in  others  decreases,  the  apparent  specific  gravity. 

In  soil  No.  530  the  results  are  very  similar  to  those  obtained  in  the 
cohesion  tests.  This  type  shows  an  increase  in  specific  gravity  up  to 
a  maximum,  above  which  point  it  decreases  to  what  has  been  assumed 
to  be  the  optimum  point.  Calcium  oxid,  superphosphate,  ammonium 
sulphate,  sodium  nitrate,  and  sodium  carbonate  decrease  the  specific 
gravity,  while  potassium  sulphate  slightly  increases  it,  differing  con- 
siderably from  their  action  on  the  previous  soil. 

With  soil  No.  516  the  results  are  similar  to  those  with  No.  530  in 
that  the  apparent  specific  gravity  increases  with  increase  in  moisture 
content  to  18.5  per  cent,  beyond  which  it  decreases  to  the  optimum 
point.  All  salts  affect  this  soil  in  the  same  manner,  resulting  in  an 
increase  in  apparent  specific  gravity,  sodium  carbonate  having  the 
greatest  effect. 

Soil  No.  428  shows  the  same  relation  between  apparent  specific 
gravity  and  moisture  content  as  soils  Nos.  516  and  530.     The  effect 


27 


of  salts  is  very  similar  and  also  tends  to  increase  this  property  to  a 
slight  extent. 

The  two  physical  properties  of  soils  known  as  cohesion  and  ap- 
parent specific  gravity  are  more  or  less  dependent  upon  and  governed 
by  the  same  factors,  and  it  is  shown  in  the  table  that  the  effect  of 
varying  moisture  contents  and  addition  of  salts  is  similar.  Both 
reach  a  minimum  at  the  point  known  as  that  of  optimum  moisture 
content,  which  is  conceded  to  be  the  stage  most  favorable  to  plant 
growth.  Hence  these  properties  are  of  special  significance  in  soil 
investigations. 


/O  /3  20 

MO/STUP£:      CONTENT 
Fig.  3.— Relation  between  cohesion,  apparent  specific  gravity,  and  moisture  content  of  soils. 

In  classifying  the  Hawaiian  types  of  soil  according  to  these  prop- 
erties, the  clay  soil  possesses  the  highest  cohesive  properties,  the  man- 
ganese silt  next,  the  sandy  soil  third,  while  the  lowest  and  hence  the 
most  easily  cultivated  is  the  silty  soil,  No.  573.  The  same  relation 
applies  also  to  the  apparent  specific  gravity  and  is  true  not  only  at 
the  optimum  moisture  content  but  also  on  the  air-dry  soils.  The 
curve  shown  in  figure  3  well  illustrates  the  relationship  existing 
between  these  two  properties  of  Hawaiian  soils.  At  the  lower 
moisture  contents  the  curves  diverge  considerably  while  above  a  given 
point  they  again  foUow  similar  lines. 


28 


VAPOR  PRESSURE. 


Comparatively  little  work  has  been  done  on  the  effect  of  soluble 
salts  on  vapor  pressure  of  soils,  i.  e.,  the  rate  of  evaporation.  Theo- 
retically salts  should  increase  the  surface  tension  of  solvents  and 
thereby  lower  their  vapor  pressure  and  hence  increase  the  water- 
retaining  capacity  of  the  soil.  The  study  made  of  this  property  indi-. 
cates  that  this  theory  apparently  apphes  to  Hawaiian  soils. 

As  a  means  of  measuring  this  property  of  soils  ordinary  weighing 
bottles  were  used.  Twenty  gram  lots  of  soil  with  which  the  various 
salts  had  been  mixed  were  placed  in  these  bottles,  12  cubic  centime- 
ters, or  60  per  cent,  of  water  was  added  to  each  and  then  allowed  to 
stand  one  week  in  the  open  air.  Weighings  were  made  at  this  stage, 
following  which  all  the  samples  were  placed  in  the  same  desiccator  with 
calcium  chlorid  and  weighings  were  again  made  after  one  week.  The 
results  are  given  in  Table  XII. 

Table  XII. — Effect  of  salts  on  vapor  pressure. 


Salts  and  fertilizers. 


Sodium  carbonate 

Sodium  nitrate 

Magnesium  oxid 

Calcium  carbonate 

Calcium  phosphate 

Calcium  oxid 

Potassiimi  phosphate 

Potassivun  sulphate 

Ammoniimi  sulphate 

Potassimn  chlorid 

Superphosphate 

Acid  phosphate 

Cottonseed  meal 

Blood 

Acid  phosphate  and  blood . . 
Potassium    sulphate    and 

acid  phosphate 

2(NH4)-14-2i 

l(NH4)-9-li 

2  (N03)-14-2 1 

Check 


Amoimt 
added. 


Gm. 
0.10 
.09 
.04 
.10 
.23 
.06 
.21 
.17 
.13 
.08 
.10 
.10 
.10 
.10 
.10 

.10 
.10 
.10 
.10 


Soil  No.  530. 


Water  retained 


In  air. 


Perct. 
65.3 
71.2 
64.2 
66.2 
52.8 
58.6 
51.4 
62.7 
73.9 
50.2 
63.3 
77.0 
32.5 
42.6 
44.0 

58.2 
36.5 
37.8 
59.6 
48.0 


In  des- 
iccator. 


Perct. 
46.0 
55.5 
43.6 
42.7 
21.0 
29.7 
26.9 
42.9 


25.6 
10.2 
10.8 
41.3 
24.6 


Soil  No.  573. 


Water  retained. 


In  air. 


Perct. 
39.4 
50.0 
45.7 
41.0 
42.7 
44.8 
41.3 
48.1 
41.7 
45.8 
44.7 
45.8 
41.5 
36.1 
31.2 

40.3 
39.3 
35.7 
45.3 
36.3 


In  des- 
iccator, 


Perct. 
20.9 
33.2 


26 

21 

15 

24, 

19 

33 

26, 

21, 

27, 

28.5 
9.7 
7.2 
4.3 

16.2 
8.3 
9.6 
25.6 
15.3 


Soil  No.  428, 


Water  retained. 


In  air. 


Perct. 
39.2 
44.1 
44.4 
44.3 
43.0 
39.8 
42.4 
39.5 
43.0 
40.2 
42.8 
41.3 
43.3 
48.7 
41.4 

49.2 
41.2 
38.7 
57.2 
37.0 


In  des- 
iccator. 


Per  ct. 
31.9 
38.8 
38.2 
35.3 
30.7 
31.5 
25.4 
31.2 
31.7 
40.5 
25.7 
15.3 
23.1 


30.3 
19.3 
17.5 
22.8 
17.8 


Soil  No.  516. 


Water  retained. 


In  air. 


Per  ct. 

Perct. 

43.7 

29.5 

46.8 

31.4 

42.9 

24.4 

44.9 

26.9 

45.7 

44.8 
35.9 
37.8 
35.6 
44.8 
38.4 
37.3 
43.6 
43.8 
40.7 

44.1 
40.6 
37.2 
42.4 
35.4 


In  des- 
iccator. 


28.3 
15.2 
17.5 
17.4 
33.8 
25.6 
22.7 
27.4 
29.9 
22.5 


20.4 
20.9 
28.6 
22.1 


1  Fertilizer  mixtures  containing  nitrogen,  phosphoric  acid,  and  potash  in  the  order  and  proportions 
(percentages)  indicated;  nitrogen  from  ammonium  sulphate  in  the  first  two,  from  sodium  nitrate  in  the 
third. 

These  figures  indicate  that  the  effect  of  salts  upon  vapor  pressure 
in  soils  is  one  of  considerable  importance.  Salts  act  upon  Hawaiian 
soils  more  or  less  according  to  theory.  The  major  part  of  them  increase 
the  water-holding  power  in  all  four  soils.  Organic  substances  in- 
creased evaporation  in  soils  Nos.  530  and  573,  but  had  the  opposite 
effect  upon  Nos.  428  and  516.  These  results  also  show  that  the  form 
of  nitrogen  used  in  mixed  fertilizers  bears  a  definite  relation  to  the 
vapor  pressure.     Those  in  which  sodium  nitrate  was  used  show  a 


29 

much  greater  capacity  for  holding  moisture.  In  fact,  sodium  nitrate 
itself  has  the  most  striking  effect  on  all  types  of  soils.  There  is  no 
apparent  classification  of  the  results  according  to  the  changes  in  sur- 
face tension  which  should  theoretically  result  through  the  addition  of 
the  salts. 

HYGROSCOPIC  MOISTURE. 

When  a  soil  has  been  dried  in  the  air  and  then  is  exposed  to  a  moist 
atmosphere  it  will  reabsorb  moisture.  The  amount  which  it  is  able 
to  take  up  depends  upon  several  factors,  such  as  mechanical  composi- 
tion, presence  or  absence  of  organic  matter  and  its  state  of  decay, 
temperature  of  the  air,  and  presence  of  colloidal  clay  and  ferric  and 
aluminum  hydrates.  This  form  of  moisture,  while  it  is  not  in  itself  able 
to  support  normal  plant  growth,  may  materially  assist  in  sustaining 
vegetation  during  drought.  Some  investigators  claim  it  to  be  of 
absolutely  no  service  to  plants. 

Hawaiian  soils,  owing  to  their  high  humus  and  ferric  hydrate  con- 
tent, possess  a  very  high  hygroscopic  coefficient.  Of  the  series  used 
in  this  study  the  sandy  soil  was  lowest,  as  would  be  expected,  but 
even  in  this  case  the  hygroscopic  moisture  is  high  in  comparison  with 
normal  sandy  soils,  due  to  its  high  organic  content. 

Table  XIII  shows  the  comparative  moisture-absorbing  power  of 
the  types  studied.  From  these  data  we  are  led  to  conclude  that, 
due  to  the  abnormal  physical  properties  of  Hawaiian  soils,  the  size 
of  particles  is  not  the  primary  factor  in  determining  its  hygroscopic 
properties,  although  surface  exposed  is  an  important  factor. 

The  data  presented  in  this  table  were  obtained  by  exposing  a  very 
thin  layer  of  soil  in  a  saturated  atmosphere  for  144  hours,  after  which 
the  total  moisture  was  determined.  Soil  No.  428  having  the  least 
exposed  surface,  the  highest  percentage  of  organic  matter,  and  the 
highest  moisture  content  in  the  air-dry  soil,  has  the  least  hygroscopic 
power.  The  clay  soil.  No.  530,  has  the  most  exposed  surface,  the 
largest  percentage  of  ferric  hydrate,  the  lowest  moisture  content  in 
air-dry  form,  the  least  organic  matter  content,  and  next  to  the  lowest 
absorbing  power.  But  soils  Nos.  516  and  573,  a"  manganese  silt  of 
high  iron  content  and  an  organic  silt,  respectively,  soils  very  dissimi- 
lar in  chemical  composition  and  physical  properties,  have  the  highest 
absorbing  power,  with  the  balance  in  favor  of  the  manganese  soil. 

Table  Xlll  .—Percentage  of  hygroscopic  moisture  absorbed  in  144  hours. 


Sou  No. 

Hygro- 
scopic 
moisture. 

530 

573 

428 

516 

Per  cent. 
19.32 
21.59 
15.  .')6 
24.  W     1 
1 

30 

Table  XIV  shows  the  effect  of  salts  upon  the  hygroscopic  power  of 
soils.  That  this  property  should  be  affected  by  the  addition  of  fer- 
tilizers was  to  be  expected,  since  most  salts  possess  this  property 
themselves  to  a  greater  or  less  extent,  and  it  is  only  natural  that  they 
should  impart  it  to  soils.  These  experiments  were  conducted  by 
exposing  a  thin  layer  of  soil  to  a  saturated  atmosphere  in  two  large 
containers.  Conditions  were  made  as  nearly  similar  as  possible,  but 
blank  samples  of  soil  were  exposed  in  each  as  checks.  Salts  were 
well  mixed  with  a  bulk  of  soil  at  the  rate  of  0.5  per  cent  of  salt,  and 
weighings  made  from  this  bulk.  Samples  were  exposed  for  48  hours 
and  total  moisture  determined  in  the  air  bath  at  105°  C. 

Table  XIV. — Effect  of  salts  and  fertilizers  on  hygroscojpic  moisture. 


Salts  and  fertilizers. 


Soil 

Sou 

Soil 

Soil 

No.  530. 

No.  573. 

No.  428. 

No.  516. 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

3.17 

10.84 

9.87 

5.54 

17.21 

19.35 

14.80 

21.40 

16.78 

19.80 

14.05 

21.30 

16.76 

17.88 

13.90 

19.90 

17.08 

18.70 

15.53 

21.15 

17.28 

24.80 

17.45 

22.20 

17.64 

24.20 

15.80 

21.30 

16.35 

18.90 

14.55 

20.70 

16.26 

20.81 

13.70 

21.20 

16.90 

20.20 

14.70 

21.50 

16.56 

22.00 

15.08 

20.50 

17.07 

20.30 

13.80 

21.40 

16.50 

18.50 

14.35 

21.80 

18.95 

32.00 

22.02 

30.00 

16.35 

18.58 

14.58 

21.10 

Soil 
No.  542. 


Original  moisture  content  of  soils 

Potassium  sulphate 

Calcium  oxid 

Acid  phosphate 

Ammonium  sulphate 

Sodium  nitrate 

Sodium  carbonate 

Check 

Calcium  sulphate 

2  (NH4)-14-2 1 

2(N03)-14-2i 

Superphosphate 

Potassium  sulphate  and  acid  phosphate. 

Sodium  chlorid 

Check 


Per  cent. 
4.12 
18.45 
16.10 
16.42 
20.30 
20.10 
17.95 
16.11 
17.30 
16.80 
17.06 
16.70 
16.60 
22.50 
16.18 


1  Fertilizer  mixtures  containing  nitrogen,  phosphoric  acid,  and  potash  in  the  order  and  proportions 
(percentages)  named;  nitrogen  from  ammonium  sulphate  in  the  first,  from  sodium  nitrate  in  the  second. 

The  effect  of  adding  salts  upon  the  ferruginous  clay  is  to  increase 
the  hygroscopic  power  in  every  instance,  except  where  calcium  sul- 
phate is  added,  in  which  case  there  is  very  little  variation.  As  a 
matter  of  fact  the  general  tendency  of  all  the  salts  on  the  different 
types  is  to  increase  this  property  of  soils,  and  in  cases  where  there  is 
a  decrease  it  is  almost  negligible.  Sodium  chlorid,  being  itself  a 
hygroscopic  salt,  imparts  the  highest  absorbing  power  to  the  soil, 
while  the  lowest  is  effected  by  addition  of  acid  phosphate. 


SUMMARY. 

The  foregoing  pages  contain  data  obtained  from  an  extensive  study 
of  the  physical  properties  of  Hawaiian  soils  and  the  effect  of  fertilizers 
upon  these  properties.  It  is  evident  that  agents  whioh  influence  the 
mechanical  condition  are  many  and  complex.  It  has  also  been  clearly 
demonstrated  that  the  addition  of  salts  or  fertilizing  materials  affects 
the  structure  of  the  soil. 

It  is  impossible  to  predict  in  all  cases  the  degree  to  which  any  one 
or  all  physical  properties  will  be  influenced  by  the  addition  of  a  fer- 


31 

tilizer,  since  this  depends  primarily  upon  the  mechanical  composition 
of  the  soil,  the  nature  of  the  organic  matter,  and  probably  upon  cer- 
tain factors  which  are  at  present  unknown.  However,  within  certain 
limits,  the  effect  of  adding  a  larger  application  of  a  salt  only  magnifies 
that  of  a  smaller  application.  Tliis  suggests  that  the  measurement 
of  the  physical  effect  may  be  just  as  accurately,  and  possibly  more 
accurately,  determined  than  the  chemical  effect.  The  measurement 
of  a  normal  application  of  fertilizer  through  a  chemical  analysis  of 
the  soil  is  practically  impossible. 

Capillarity  is  diminished  in  clay  soils  by  the  addition  of  salts  but 
increased  in  sandy  soils.  Also  this  property  is  more  active  in  silts 
than  in  sandy  or  clay  soils,  being  slowest  in  the  latter. 

The  percolation  of  water  is  most  rapid  in  sandy  soils  and  slowest 
in  types  the  particles  of  which  are  most  likely  to  swell.  Fertilizers 
considerably  increase  the  resistance  to  percolation.  The  theory  that 
soils  of  greater  capillary  activity  offer  the  least  resistance  to  perco- 
lation of  water  does  not  apply  to  Hawaiian  soils. 

Salts  increase  or  diminish  the  size  of  the  soil  aggregates.  This 
is  of  no  small  importance  in  the  use  of  fertilizers. 

The  cohesion  of  the  soil  particles  in  most  instances  is  increased  by 
the  addition  of  salts.  This  is  also  true  of  the  apparent  specific 
gravity.  However,  there  are  too  many  exceptions  to  make  any 
definite  statement. 

The  hygroscopic  moisture  is  increased  by  the  addition  of  salts, 
with  but  very  few  exceptions. 

The  vapor  pressure  is  lowered  in  most  instances,  but  can  not  be 
explained  from  a  consideration  of  the  surface  tension  of  the  added 
salts. 

Acknowledgments  are  due  and  thanks  hereby  extended  to  Dr. 
W.  P.  Kelley  for  valuable  suggestions  and  for  interest  shown 
throughout  this  investigation. 


ADDITIONAL  COPIES 

OF  THIS  PUBLICATION  MAY  BE  PROCURED  FROM 

THE  SUPERINTENDEXT  OF  DOCUMENTS 

GOVERNMENT  PRINTING  OFFICE 

WASHINGTON,  D.  C. 

AT 

5  CENTS  PER  COPY 
V 


UNIVERSITY  OF  FLORIDA 


3  1262  08929  1016 


